The present invention relates to through-glass type antennas, and more particularly to such antennas which mount on a window of a vehicle for two-way radio or cellular telephone communication.
Cellular telephones commonly are used for mobile communication with passengers in vehicles. Such telephones usually have a hand-held unit which includes a microphone, a small speaker and a keypad for placing calls and controlling the operation of the telephone. The hand-held unit is coupled by a cable to an electronics module that contains a radio frequency transceiver. The transceiver is coupled to an antenna on the exterior of the vehicle to send and receive the radio frequency signals. Cellular telephones transmit in the 825 to 845 MHz frequency band and receive signals in the 870 to 890 MHz frequency band.
A typical cellular telephone antenna for a motor vehicle is attached to the exterior surface of a window and comprises a short section of rigid wire extending vertically from the vehicle body. A coupling box is mounted on the interior surface of the window opposite to the antenna and is connected by a coaxial cable to the transceiver. The coupling box and the antenna are electrically coupled so that signals from the transmitter section of the transceiver are coupled to the exterior wire from which the signals radiate. The coupling also allows radio frequency signals to be received by the exterior element and applied to the receiver section of the transceiver.
Even though such cellular telephone antennas are relatively short, protruding approximately one foot from the surface of the vehicle, they are subject to accidental breakage and acts of vandalism. Although cellular telephone antennas are considered by some people to be a status symbol, others may consider them to be unsightly and a detraction from the aesthetic appearance of the vehicle.
U.S. Pat. No. 5,041,838 discloses a low profile, flat disk-shaped antenna for cellular telephone usage. This antenna is attached to a horizontal exterior surface of the motor vehicle, such as the roof. A coaxial cable extends through a hole in that surface, connecting the external antenna to the transceiver inside the motor vehicle. Although this antenna was relatively inconspicuous and eliminated some of the aesthetic drawbacks of previous cellular telephone antennas, it required a hole through the body of the motor vehicle for the coaxial cable. Vehicle owners may be hesitant to drill a hole for a cellular telephone as the hole would have to be filled if the cellular telephone was later removed from the vehicle.
It is therefore desirable to create a low-profile antenna which does not require that a hole be drilled through the vehicle body.